The present invention generally relates to combustors for gas turbine engines and, more particularly, to cooling schemes for combustor domes.
Gas turbine combustion systems operate in extreme temperature environments, which ultimately limit the service life of the component. Cooling techniques are employed to lower the metal temperatures of combustor components to acceptable levels for durability and life. One of the most critical regions requiring cooling is the dome area.
Methods for cooling a combustor dome are described in U.S. Pat. No. 3,705,492. The dome cooling methods described are splash louver type designs whereby air is admitted through relatively large ports in the dome. The air impinges on deflector plates such as to direct the air in a circumferential manner. Although the described methods may be used for dome cooling, they require a large amount of cooling air. Cooling air in the dome region not only plays a part in mitigating wall temperatures but also interacts with primary zone aerodynamics. Typically, an excess of cooling air will adversely affect primary zone performance, particularly in the case of a rich quench lean (RQL) combustor. Further, a disproportionate amount of air required for dome cooling reduces the overall air budget required for cooling and performance of other components.
Another method for cooling a combustor dome is described in U.S. Pat. No. 5,307,637. The disclosed method comprises a baffle or heat shield having an inverted L-shaped ring. The '637 patent employs backside impingement cooling air at the ring to create a starter film for the downstream effusion cooling holes on the dome plate. The subsequent effusion cooling holes are then directed in a radially outward pattern from the center position of the injector aperture. In the absence of a starter air flow, film cooling effectiveness for radial effusion is low in the initial flow region and increases as one travels radially outward. The initial low film effectiveness is because radial effusion requires several rows of effusion holes for the cooling film to develop. Each individual effusion row by itself provides little protection, but it is only when the effect of a number of rows are superimposed on each other that sufficient thermal protection is provided. Although the starter film provided by the impingement air is designed to compensate for the initial low film effectiveness at the beginning of the radially directed cooling film, impingement cooling is less efficient than effusion cooling. Due to the low efficiency of impingement cooling the described method is not suitable for some applications.
Another method for cooling a combustor dome is disclosed in U.S. Pat. No. 5,918,467. The '467 patent describes a cooling scheme for a combustor heat shield comprising a multiplicity of small cooling holes in a preferential orientation. The heat shield is subdivided into four regions and transition areas, which bound the uniform effusion hole orientation in a given zone. The goal of the oriented effusion holes is to effectively cool all regions of the heat shield and complement the swirl created by the fuel injector air. Although the described method does not require creating a starter film with impingement air, it does require attaching a heat shield to the dome. Because the heat shield adds weight and manufacturing complexity to the dome, it is unsuitable for some applications.
As can be seen, a need exists for more efficient cooling schemes applied to the dome of a gas turbine combustor. Simplified cooling scheme designs are desirable due to beneficial manufacturing cost impacts. Cooling schemes requiring reduced amounts of cooling air are needed. Further, cooling methods are needed that do not require additional components, such as heat shields and louvers.